1. Field of the Invention
The present invention relates to a motion compensation device that detects motion caused by motions, induced by, for example, camera motion, and compensates for the motion to prevent image blur on an image forming plane, and, more particularly, to a camera system, including a camera body, and a tens barrel equipped with a motion compensation device.
2. Description of the Related Art
In recent years, electronification of various components of a camera, including automatic exposure and auto focus functions, has produced highly automated camera systems. With such camera systems, attempts have been made to automate an anti-motion function (also known as a motion compensation function) that compensates for image blur caused by camera motion during hand held photographic operation. Image blur suppression devices have as their object, suppression of, or reduction of, blurring in an image projected onto an image plane. A motion compensation device is a type of image blur suppression device which compensates for motion incident upon an optical system which projects the image onto the image plane. Motion is typically imparted to the optical system by way of vibrations in the optical system, or in the surrounding holding member. In general, known motion compensation devices cause a compensation lens to shift counter to the motion of the optical system so as to shift the image projected by the optical system relative to the optical system.
Generally, known motion compensation devices for cameras comprise a motion detection unit that detects motions based on the camera's angular velocity or acceleration, a motion compensation optical system, provided within a lens barrel attached to the camera, movable over a plane perpendicular to the optical axis of the main optical system, a computation unit, such as a microcomputer, that computes a compensating value (including, for example, direction and velocity), to correct a photographic optical axis, based on output provided by the motion detection unit, and a drive unit, including an electric motor, etc., to move the motion compensation optical system vertically and horizontally based on the computation results from the computation unit.
Image blur is compensated for by shifting the motion compensation optical system over the plane perpendicular to the optical axis of the main optical system during a motion compensation sequence. Other representative methods of motion compensation used in cameras are, for example, the gimbal method and the variable angle prism method wherein a liquid is placed between two glass plates, and the angle formed by these two glass plates is adjusted. In general, the camera body controls a photographic operation by obtaining data, such as a focal length of the lens and an aperture value, along with status data, such as whether the focal point detection is in automatic or manual mode, and the movement status of the movable lens, obtained from the lens barrel.
Communication between the camera body and the lens barrel is achieved by sending and receiving serial communication signals between microcomputers, one on the camera body side and another on the lens barrel side. The signals are transmitted via contact points that makes contact when the camera body and the lens barrel are assembled together.
However, in known motion compensation devices a possibility exists that when the camera body instructs the lens barrel to initiate motion compensation control, even if motion detection was impossible because, for example, a power supply was inadvertently shut off to either a motion sensor or to a motion detection system circuit provided within the lens barrel. Moreover, even if power is resupplied to the motion sensor and the motion detection unit, there is the possibility that the camera body might initiate a motion compensation sequence without stabilizing the output of the motion detection system circuit, i.e. before initialization of the motion detection system circuit. In such an event is impossible to determine whether a sufficiently stable output can be generated.